Hereinafter, the background art will be described with reference to FIGS. 1 and 2.
FIG. 1 is a view schematically showing the configuration of a conventional car audio system in which a passive antenna for a vehicle is connected to a car audio device through a coaxial cable.
As shown in FIG. 1, when a passive antenna is used as an antenna for a vehicle, the gain of the antenna is improved. However, since the antenna protruding toward outside is formed to have a length satisfying a frequency band for operating broadcast signals, it is not good for outer appearance of the vehicle, and physical damage is worried. In addition, if a driving gear for adjusting the length of the antenna operates when the power of the car audio device is turned on and off, cost of the car audio device is increased, and risk of failure is also increased.
In addition, since the broadcast signals received through the passive antenna are transferred to a broadcast tuner embedded in the car audio device through a coaxial cable, the received broadcast signals can be degraded in correspondence to the loss rate of the broadcast signals transferred through the coaxial cable.
FIG. 2 is a view schematically showing the configuration of a conventional car audio system in which an active antenna for vehicle is connected to a car audio device through a coaxial cable.
As shown in FIG. 2, the car audio system in which an active antenna is connected to a car audio device through a coaxial. Cable is a car audio system using an active antenna which is referred to as a Glass antenna or a Micro antenna. The car audio system uses a low noise amplification unit to improve receive sensitivity of the antenna, and accordingly, a separate power line is needed to supply power.
Here, when an active antenna is used, the antenna size is reduced compared with the case of using a passive antenna, and thus physical damage can be prevented, and aesthetic sense of the outer appearance is improved. In addition, sine a low noise amplification unit is used, reduction in the receive sensitivity caused by the reduction in the antenna size is compensated.
However, even when the active antenna is used, the broadcast signals are degraded since the broadcast signals are transferred to the tuner unit embedded in the car audio device through a coaxial cable.
That is, in the conventional car audio system in which an antenna for a vehicle transfers the broadcast signals to the tuner unit embedded in the car audio device through a coaxial cable, a coaxial cable of 75Ω having a length around 5 meters is used to transfer the received broadcast signals to the car audio device, and thus cable loss occurs. In addition, since the car audio device is arranged near the engine room of the vehicle, the tuner unit mounted on the car audio device is affected by electrical noise, which is generated by the engine or the driving motor of the vehicle to have a frequency band close to a broadcast frequency, and thus receive sensitivity of the broadcast signals is degraded.
Accordingly, a practical and useful technique for preventing the cable loss generated in the coaxial cable connecting the antenna and the car audio device of the vehicle and improving the receive sensitivity of the broadcast signals is earnestly required.